Recently, resin molded products are widely used as components of various products such as vehicles, electric/electronic equipment, office automation (OA) equipment, household electrical appliances, building materials, sanitary goods and the like. These products are usually composed of assemblies of a plurality of parts, and these parts are often arranged adjacent to each other or in contact with each other by fitting, abutting, overlapping, fastening with a screw or the like. Snap-fit structure is known as one of the modes of obtaining such assemblies (Patent Document 1), but is problematic in that resinous nail portions are often broken if the parts constituted by molded articles are insufficient in impact resistance.
Further, it is known that the above-mentioned assemblies generate squeaking noise (rubbing noise) when the adjacent parts are dynamically contacted with and rubbed against each other by the action of vibration, rotation, twisting, sliding, impact and the like. For example, squeaking noise may occur due to rubbing of a blowing outlet of an air conditioner or audio housing part disposed in an automobile against a part fitted in the periphery or inside thereof due to vibration or the like. The above-mentioned squeaking noise is known as unpleasant sound caused by the stick-slip phenomenon generated when two objects are rubbed against each other, and thus is caused by a property different from slidability of resins.
Also, in recent years, superior appearance is demanded for products in the field of vehicles, OA equipment, precision equipment, household electrical appliances, furniture, daily necessaries, toys, etc., from the viewpoint of high quality and differentiation. Thus, thermoplastic resinous parts adapted to the products in these fields are required to be excellent in appearance. Plating is known as a method for giving an excellent appearance to a thermoplastic resinous part. However, there is a problem such that when the plated resinous parts are used in association with each other, scratching or peeling may occur in sites where the plated surfaces come into contact with each other, so that appearance may be impaired, or the above-mentioned squeaking noise may occur.
The stick-slip phenomenon is understood as a phenomenon in which frictional force largely varies periodically as illustrated in FIG. 11; and more specifically, it is generated as illustrated in FIG. 12. That is, when an object M connected with a spring is placed on a driving table that moves at a driving speed V, as illustrated by a model of FIG. 12(a), the object M moves toward the right direction first as illustrated in FIG. 12(b) together with the table moving at the driving speed V by the action of a static frictional force. When the spring force by which the object M is to be restored to its original position becomes equal to the static frictional force, the object M starts to slip in the opposite direction to the driving speed V. At this time, the object M comes to receive a kinematic frictional force, and the slip is stopped when the force of the spring becomes equal to the kinematic frictional force as illustrated in FIG. 12(c), so that the object M comes again into a state where it attaches on the driving table and it moves again in the same direction as the driving speed V (FIG. 12(d)). This is called a stick slip phenomenon, and it has been argued that, as illustrated in FIG. 11, if the difference Δμ between the coefficient of static friction μs and the lower end of a saw wavy form μl is large, squeaking noises tend to be generated easily. Meanwhile, a dynamic friction coefficient is a middle value between μs and μl. Therefore, even when the absolute value of the static friction coefficient is low, squeaking noise becomes liable to occur, if the Δμ is large. Such squeaking noise becomes a main cause for impairing comfortableness and quietness inside and outside the automobile cabin or inside the office or house room, and reduction of squeaking noise is strongly demanded.
Conventionally, it is known that a rubber-reinforced aromatic vinyl resin reinforced with a crystalline rubber such as an ethylene/alpha-olefin rubber is used as a molding material to prevent molded articles from generating squeaking noise (refer to Patent Document 2 and Patent Document 3). However, the molded articles obtained from the above molding material is inferior in platability and is still insufficient in appearance, compared with rubber-reinforced aromatic vinyl resins reinforced with diene rubbers such ABS resins.
Conventionally, it is known that a predetermined amount of a polypropylene resin is blended to obtain an alloy so as to improve the platability of the rubber-reinforced aromatic vinyl resin reinforced with a non-diene rubber (Patent document 4). However, it is found that when an article is constituted by assembling a plurality of parts which are molded products made from the above alloy and plated, the plated surfaces of these parts are hurt or generate unpleasant sounds such as squeaking noise in the case where the plated surfaces contact with each other.